The present invention relates to a method and apparatus for producing screw feeders for use in a plastic injection-molding machine, wherein the screw feeder includes a shank having a spiral integral lengthwise therewith. As the shank revolves, the turning spiral feeds a material placed in a cylindrical container, wherein the material includes a powder, pellets, or a slurry-like substance.
To feed a powdery or pasty material the common practice is to employ a pneumatic conveyor which consists essentially a hopper and a compressed air intake device both provided at one end of a cylindrical container, and a separator provided at the other end thereof. The separator is intended to separate the air from the material. The compressed air is intermittently supplied and feeds the material.
One disadvantage of this known conveyor system is that the mechanism becomes complicated because of the provision of the air intake device for intermittently introducing compressed air and the separator for separating the air from the material. Another disadvantage is a low feeding speed because of the necessity of mixing air with the material. The known injecting die is fixed to a mouthpiece, so that the molded objects passed therethrough have a constant cross-section.
The present invention is directed toward a method and apparatus for producing screw feeders for use in a plastic injection-molding machine which solve the problems discussed above. Thus an object of the present invention is to provide a method and apparatus for producing screw feeders on mass-production basis.
This object is achieved by providing an apparatus which comprises a stationary die provided in a material conveying cylinder, a rotary die provided coaxially in the cylinder, the stationary die being located inward of the rotary die, the rotary die including an opening in the center, the inner surface defining the opening including a groove produced obliquely with respect to the axis of the rotary die, the stationary die taking the form of a top having a head and a leg extending through the opening of the rotary die, and means for driving the rotary die.
The object of the present invention is also achieved by providing another version of the apparatus which comprises a molten material storing chamber located in an injecting opening of a cylinder, the material storing chamber including a pair of apertures having a common axis perpendicular to the direction in which the molten material is extruded, the pair of apertures being adapted to support a core rod rotatively, a rotary die provided in one of the apertures, the rotary die having an opening in the center so as to allow the molten material to pass through, the inner surface defining the opening including a groove produced obliquely with respect to the axis of the rotary die, and means for driving the rotary die.